What is the small button on the Aircable / Airserial for? Is it a "reset" switch?

The small recessed button on the Aircable / Airserial device is not a reset switch. Pressing it will put the device into master mode, where it will attempt to automatically pair with another nearby Aircable device. It is not used in a typical astronomical environment.

If you press this button accidentally, simply press it again to return the device to its original state.